Process for detinning lead alloys



till

Patented June 9 1936 PROCESS FOR DETINNING LEAD ALLOYS Thomas D. Jones, Metuchen, N. L, and John C.

Reinhardt, Omaha, Nebr., assignors to American smelting and Refining Company, New York, N. Y., a corporation of New Jersey No Drawing. Application May 21, 1935, Serial No. 22,558

6 Claims. (CI. 75-78) This invention relates to the treatment of tinbearing lead and lead alloys, for example, various type metal compositions, tin-bearing antimonial leads, solders, etc., and the reclaimed scrap from such products.

An important feature of the present invention is the novel manner in which the tin is extracted from the alloy and concentrated in an inert carrier slag as tin oxide. Briefly, this result is at.- tained by oxidizing the tin from a bath of the metal with lead oxide produced in situ in the slag by reacting the slag or a constituent thereof with a reagent such as lime or its equivalent.

Other features and" advantages of the invention will be readily apparent from the following particular description and the appended claims.

The invention may be readily practiced, using standard apparatus, as follows: the lead alloy containing tin is melted and dressed to assure a clean surface. The slag, which initially provides lead oxide in situ by appropriate chemical reaction for converting the tin to oxide and which also serves as the vehicle in which the tin oxide is concentrated, is next added to the bath. The slag comprises lead chloride and contains enough of that compound to provide sufiicient lead oxide to convert the tin content of the bath to oxide. Sodium chloride, which lowers the melting point of the slag, is a highly desirable constituent thereof.

With the bath and slag liquid, lime or its equivalent is incorporated, the lime reacting with the lead chloride content of the slag to form lead oxide in situ, the latter in turn converting the tin to tin oxide which enters the slag and is mechanically carried thereby. The other products of reaction, namely lead and calcium chloride, enter the bath and slag, respectively. The bath, slag and lime are, of course, intimately mixed throughout the operation by means of a mixing machine which may be of the type that creates a vortex in the bath. If so, the lime is conveniently added via the vortex and at intervals to avoid undue thickening of the slag.

The tin oxide concentrated in the slag, as a result of the reaction of the tin content of the bath with the freshly formed lead oxide, is substantiaily free from such elements as arsenic, antimony, bismuth, copper, selenium, tellurium and precious metals which may be present with the tin and lead in the original metal. The tin value of the slag is readily recovered as by lixiviation oi the slag with water to dissolve the soluble constituents and smelting of the residue with coke to yield a metal of high tin content. Other recovery processes can, of course, be employed.

The following specific example will further illustrate the process of the invention: 192,000 parts by weight of a tin-bearing lead alloy were melted and treated successively with five batches of slag, in the manner hereinafter described, each batch comprising 7,950 parts by weight of lead chloride fume (86% PbClz) and 1281 parts by weightof sodium chloride. There were finally recovered 21,000 parts by weight of granulated dry slag 3 and. 173,000 parts by weight of detinned metal. The original metal, tin slag and final metal analyzed as follows:

The operation with each of the five batches of slag was as follows: after melting and drossing the lead alloy, the lead chloride fume and sodium chloride were mixed and melted on the molten 30 metal. The mixer was started and 1030 parts by weight of quicklime added at the rate of '100 parts by weight per hour, the mixing being continued for about two hours after the lime addition. The lime is preferably less than one-quar- 35 ter inch mesh and the temperature of operation will vary from approximately 1000 F. at the start of the operation to approximately 825 F. as the calcium chloride builds up and approaches eutectic proportions with the sodium chloride. 40

Upon completion of the reaction period foreach batch, the slag was removed from the detinning kettle and charged in liquid form to a purifying kettle in which it was stirred for a period of from four to five hours over a bath of low-antimony lead to remove metal prills of relatively high arsenic and antimony content from the slag. Thereafter the slag was ladled into water to granulate it and leach out the soluble components, the aggregate of these five batches of granulated slag Slugs prior to purification Batch Percent Percent number antimony arsenic Percent tm Percent lead Metal after skimming slag Batch Percent Percent number antimony arsenic Percent tm Percent lead 1 20. 6 7. 2 3. 1 Balance 2 20. 6 7. 2 2. 3 Balance 3 20. 0 7. l 0.98 Balance 4 20. '0 7. 1 0. 10 Balance 5 19. 7 6. 1 0. 1O Balance Purified s'lags before granulation Batch Percent Percent number antimony arsenic Percent m1 Percent lead It will thus be appreciated that the present invention provides an efllcient process for detinning lead alloys, the term lead alloys being used in the specification and claims to denote not only alloys of lead and tin but also alloys of these two metals with one or more other metals as hereinbefore indicated.

What is claimed is:

1. The process for detinning a lead alloy which consists in mixing a bath of said alloy and a slag comprising lead chloride and lime thereby concentrating tin as tin oxide in said slag.

2. The process for extracting tin from a lead alloy which consists in converting the tin to oxide by intimately contacting a molten bath of the alloy and a slag comprising lead chloride to which is added a reactant for producing lead oxide in situ in the slag.

3. The process for treating lead alloys containing tin which comprises establishing a molten bath thereof under a slag comprising lead chloride and sodium chloride, adding lime thereto and mixing the metal and slag thereby concentrating tin oxide in the latter.

4. The process for treating tin-bearing lead which comprises establishing a molten bath thereof under a slag comprising lead chloride and sodium chloride, adding to the slag a reagent capable of reacting therewith to form lead oxide in situ and contacting same with the bath thereby converting the tin to oxide and collecting it in said slag.

5. The process for treating a lead alloy containing tin which consists in adding a slag comprising lead chloride to a bath of such an alloy, oxidizing the tin content of the bath with lead oxide formed in situ in the slag by incorporating lime therein, separating the resultant slag from the bath and purifying the slag by stirring same 5 

